Method and apparatus for simultaneous aural and panoramic radio reception



M. WALLACE EVAL Aug. 14, 1945. 2,331,940

METHOD AND APPARATUS FOR SIMULTANEOUS AURAL AND PANORAMIC RADIO'RECEPTION f Filed July 17 1941 6 Sheets-Sheet 1 Aug' 14' 1945" M.WALLACE ET Al.

METHOD AND APPARATUS FOR SIMULTANEOUS AURAL AND PANORAMIC RADIO REcEPToNFiled July 17 1941 6 SheetS-Sheet 2 QNEESQQ IN VEN TORS` JQQBT y f N 1 0w WM v n a i@ am Wm 9 OMS ad ma 9%. YI e Aus-14,1945 MWALLA'CE Em2,381,940

METHOD AND APPARATUS FOR SIMULTANEOUS AURAL AND PANORAMIC RADIORECEPTION Filed July 17, 1941 6 Sheets-Sheet 5 if@ f5 62 7/ f L 6*/ 1F:can.. E C da da 63a 551 70 54 INVENTORS @nieuwe/e gif/Mace?) o/zace/SJ/fav,

Aug- 14, 1945- M. WALLACE ET AL 2,381,940

METHOD AND APPARATUS FOR SIMULTANEOUS AUHAL AND PANORAMIC RADIORECEPTION Filed July 17 1941 6 Sheets-Sheet 4 Aug' 14 1945' M. yWALLACEET A1.

2,381,940 AURAL METHOD AND APPARATUS FOR SIMULTANEOUS AND PANORAMICRADIO RECEPTION Filed July 17 1941 6 Sheets-Sheet 5 HIW @WARN SN@ DK INVEN TORS M N c M mm@ .az www me t naamw 1h 8AM 90,.,6 2e m MS Dun 6 Aug'14 1945' M. WALLACE ETAL METHOD AND APPARATUS FOR AND PANORAMIC RADIORECEPTION Filed July 17, 1941 INVENTORS n. M W m Q. W MU ma PatentedAug. 14, 1945 METHOD AND APPARATUS FOR SIMIUL- TAN EOUS AURAL ANDPANORAMIC RADIO RECEPTION Marcel Wallace, New York, N. Y., and Horace G.

Miller, Belleville, N. J., assignors, by mesne assignments, to saidWallace, doing business as Panoramic Laboratories, New York, N. Y.

Application July 17, 1941, Serial No. 402,822

20 Claims.

Our invention relates to improvements in methods of panoramic receptionand to methods of simultaneous aural and panoramic reception.

One of the objects of our invention is to provide greater facility formanually tuning a panoramic radio receiver over wide frequency ranges,while maintaining a substantially constant visual bandwidth.

Another object of our invention is to provide means for effecting auralreception over a narrow band of frequencies and simultaneous panoramicreception of a wider portion of the spectrum.

Still another object of our invention is to provide, in combination withan ordinary'radio receiver, means for panoramically receiving a wideportion of the frequency spectrum, including that portion over which theordinary radio receiver is tuned, without affecting the aural receptionthrough that receiver.

Another object of this invention is to provide a panoramic receiverhaving variable visual bandwidths and variable resolution.

Other and further objects of our invention reside in the variousarrangements of panoramic receiving systems described more fully in thespecification hereinafter following, by reference to the accompanyingdrawings, in which: Figure 1 represents a block diagram of a combinationof tunable channel which is common to an aural channel and a visualpanoramic channel; Fig. 2 represents the response curve of variouscircuits employed in the receiving system of our invention; Figs. 3a, b,c, represent the screen of a panoramic receiver for three positions ofthe controls of the tunable channel; Fig. 4 represents the shape ofdeflections on a screen with various frequency sweep velocities; Fig. 5represents the type of voltage sweep required for variable resolutionreception; Fig. 6 represents a schematic diagram of a panoramic channel,adapted to an ordinary super-heterodyne radio receiver; Fig. 7represents a schematic diagram of a wide band panoramic radio receiver;Figs. 8a, b, c, represent various views of a synchronous vibratingcondenser; Fig. 9 represents a diagram of a radio receiver using such asynchronous vibrating condenser; and Fig. 10 is a block diagram of amulti-channel receiver embodying our invention.

In the copending patent applications of Marcel Wallace, Serial Number196,520, filed March 17, 1938, now Patent 2,279,151, granted April 7,1942, for Panoramic radio receiving system, and Serial Number 204,470,filed April 26, 1938, now Patent 2,273,914, granted February 24, 1942,for Radio (Cl. Z50- 20) l0 element connected in the same tuningcircuits,

for manually tuning the receiver over the desired portion of thefrequency spectrum.

For a further and better understanding of the nature and applications ofour invention, reference is made to the copending patent applications ofMarcel Wallace, Serial No. 330,763, filed April 20,1940, now Patent No.2,312,203, for radio beacon and panoramic reception system, and SerialNo. 357,814, filed September 21, 1940, for Radio altimeter and panoramicreception system.

For example,` in the case of Fig. l of Marcel Wallaces copending patentapplication 196,520, (Patent 2,279,151)V supra, the condensers 3 and 4are periodically tunedand condensers I and 2 are manually tuned. Such anarrangement presents the disadvantage that the frequency sweep is notconstant over the entire manually tunable range. When the condensers I,2 are open, the frequency sweep on the visual bandwidth produced .causedby the rotation of 3, 4 is greater than when the condensers are closed.

In fact, this visual bandwidth decreases proportionally to the cuberatio of the mean frequency of the oscillator. For example, if the meanfrequency of the oscillator is F1 with the condenser 2 open and F2 withthe condenser 2 closed, the ratio between the two respective visualbandwidths W1 and W2 will be WT F2 In other words, the signals willspread apart on the screen as the condenser is closed. This 5 is notdesirable when it is necessary to use a fixed frequency calibration overthe screen of the receiver, which should permit instantaneousdetermination of frequency difference over wide tuning ranges.

Considerable improvements of the panoramic one of these oscillators, andperiodic tuning to the other. irrespective of the sequence in which thisis done.

Fig. 1 shows in the form of a block diagram. one example of theprinciples-used in such a double conversion panoramic receiver.V Thisblock diagram is divided into three parts surrounded by dotted lines,representing three channels which are marked respectively: Tunablechannel, Aural channel and Panoramic channel. The various elements areshown connected. forming a complete. simultaneous, aural and panoramicreceiving system. It must be understood, however, that these variouschannels can be combined two by two or can be used singly, for definiteuses, as more fully explained hereinafter.

The Tunable channel comprises:

A signal input circuit which may include an R. F. amplifier containingone or several stages, a nrst mixer receiving lsignals from said signalinput circuit and a nrst oscillator feeding signals into said mixer. Theoscillator, or any other of these three elements may be tunedeithersingly or by means of ganged variable condensers, or other type oftuner.

The Aural channel which is coupled to the output of the nrst mixercomprises an. ordinary, sharply tuned, intermediate frequency amplifiertuned to frequency F1, a detector and audio frequency amplifier and anaural responsive device, such as the telephone receivers shown. It willbe shown that this aural channel need not be tuned to exactly Fi, but toany frequency within a band extending equally on each side of F1 andthat a tuning control in .the said aural channel has certain importantapplications.

'Ihe Panoramic channel" which is also coupled in the output of the firstmixer, is in effect a panoramic receiver, frequency band psig*- Such apanoramic receiver may -be constituted by a single amplifying stageperiodically tuned, as shown yin the Marcel Wallace Patent 2,279,151,either by electronic means (Fig. 4) or by mechanical means (Fig. 14) orit may be constituted of a series of cascaded amplifying stages,similarly periodically tuned, or by a complete Superheterodyne circuitsuch as shown on Fig. 1 of Patent 2,279,151 or Fig. 4 of Patent2,312,203. Such a. super-heterodyne type of Panoramic channel comprisesa second mixer stage which, in the example chosen, is tuned to pass a.band of frequencies of W cycles, but which is centered at the frequencyof the aural intermediate frequency ampliiier. (It will be shown thatthis need not necessarily lbe centered and that a tuning control in theoutput oi' this panoramic channel has certain applications). In otherwords, this second mixer will pass a band of frequencies between f l(rz-3g) and (A+-Y2K) 'I'he relationship between frequency andampliilcation in this Panoramic channelis explained with the aid of Fig.2: In order to compensate for the sharpness of the response over a bandof W cycles, as shown by curve a, due to the selectivity of the radiofrequency stages in the Tunable channel, the coupling transformers usedin the second mixer are made to increase the amperiodically tunable overa.

pliflcation on the extreme ends of the band and to attenuate the center;this is shown by curve b. Compensation can be obtained in this mannerand the resultant over-all amplification can be made to be substantiallyconstant for a given frequency range through the entire band W as shownby curve c.

Separate controls can be used in the coupling transformers to modify theshape of curve b to suit any desirable condition, according to thevariations of the selectivity curve a for various ranges of thefrequency spectrum.

The signals from a second oscillator are fed into the second mixer.'I'his oscillator is automatically and periodically tuned overapredetermined frequency band W cycles wide, between W W Foand Fri- (inwhich Fo represents a fixed mean frequency). 'I'he signals resulting inthe output of the second mixer, which can be either the sum or thedifference between the signals fed therein, are fed into a secondintermediate frequency amplifier having one or several stages. tuned toeither this sum or difference. This ampliner (2nd I. F. Amp.) is sharplytuned and has a narrow pass band characteristic. A series of periodicimpulses will result in its output, corresponding to the signals presentover the band covered by the second mixer stage. These impulses arerectified and amplified in one or several amplifier stages (Det. amp.)and the resulting impulses are applied to one set of deflecting platesof a cathode ray oscillograph.

The second oscillator is periodically hined over a desired range, bymeans of a periodically varying frequency controlling element, markedFreq. contro which may be a tube, an inductance, a condenser, etc.,winch, in its turn, is submitted to a periodic variation by means of avoltage sweep source. This may consist of a motor and/or a source oi'periodically varying voltage. A sweep voltage synchronized with thefrequency sweep of the second oscillator is amplified, if desired, andthen applied to another set of deecting plates in the oscillograph tube.

It can be readily seen that the mere combination of the Tunable channel"and the "Aural channel" described above, constitutes an ordinarysuper-heterodyne radio receiver. The "Panoramic channel in itselfrepresents then a complete device which can be connected to such anordinary radio receiver in the output of its first mixer and constitutesa valuable attachment or adapter to such a receiver.

As the receiver is manually tuned through its tuning range, and whilethe operator listens briefly to each station in turn. a band of aconstant width of W cycles passes in view and all the other signalspresent within that band appear on the screen of the cathode ray tube asindividual inverted V deflections of various amplitudes determined bytheir respective signal strength. The linear intervals between deectionscan be made directly proportional to their frequency separation and thisrelationship is maintained throughout the tuning range of the receiver,which is a very important advantage.

A vertical reference line across the center of the screen corresponds tothe frequency to which the receiver is tuned. Amplitudes are measured onthis line. A horizontal line across the screen serves as the frequencyreference. It can be calibrated in kilocycles (positively andnegapassing tively) on both sides of the vertical line corresponding toW/2 kilocycles above and below the frequency to which the Tunablechannel is tuned. A zone limited by two parallel vertical lines on eachside of the vertical center line, indicates the Aural zone, or theaudible range usually covered by the receiver. All deflections throughthis zone on the screen are heard in the loud speaker or phones of thereceiver.

This is illustrated in Figs. 3a, b, c. Fig. 3a shows signal A in theaural zone. Signal B, C, D, E are higher in frequency, whereas F, G, H,J are lower. The frequency of each signal can be determined byalgebraically adding to the dial reading of the receiver the number ofkilocycles read on the screen, below its corresponding peak. Fig. 3bshows the receiver tuned a few kilocycles higher. Signal C has enteredthe aural zone. New signals K and L are visible, whereas signals G and Hare out of the visual range of the new band covered.

Fig. 3c shows the same screen after tuning the receiver again higher infrequency. The two signals D and E which intersect at the base, butwhich can still be visually resolved, are both within the aural range,and, therefore, are heard in the receiver with a sharp heterodynewhistle. C. W. signals only a few kilocycles apart can be separatedvisually, even if those signals cannot be separated aurally, as it willbe shown further below.

A panoramic adapter such as described hereinbefore, is limited generallyto a visual bandwidth which cannot exceed greatly the passbandcharacteristics of the manually tunable channel. This varies accordingto the type of receiver, the number and type of R. F. stages and thefrequency of operation. Most receivers will have a wider passband athigh frequencies than at lower frequencies.

The adapter can have. means for varying the bandwidth W, eithercontinuously or discontinuously, as it has been shown in previousapplications. The electronic methods of sweep lend themselves mostreadily to these variations.

Frequency resolution- As the visual bandwidth of a panoramic receiver isincreased, or decreased, the deflections on the screen of the receiverrespectively become narrower or wider. The selectivity, or frequencyresolution, of those deflections will also vary. Generally a wide bandpanoramic receiver has less frequency resolution than a narrow bandreceiver, and while the first one permits a more rapid check up of wideregions of the frequency spectrum, the second one permits more accuratecheck up when the stations are quite close to each other.

The resolution of a panoramic receiver is determined by the shape of thedeflections produced by each signal and the linear separation betweenthose deflections.

While the separation is a function of frequency distribution on thescreen, the shape of each deflection'is dependent upon two factors: astatic and a dynamic factor. The static factor is the selectivity p (incycles) of the intermediate frequency and video channels, when thevisual bandwidth is reduced to a minimum. In our numerical examples andclaims which follow we define the static resolution p of a panoramicreceiver as the passband of the filters following the periodically tunedreceiving circuit, represented as the difference of frequency, read onthe frequency sweep axis, of a panoramic receiver sweeping a frequencybandwidth of very low value, said difference of frequency being readbetween two points on the deflection produced by a single signal,points, which are at 70% of the maximum amplitude H of that deflection.

The dynamic factor r is also measured in cycles and is a function of"frequency velocity (V) which is defined by the value:

A F At in which: AF is the variation of instantaneous frequency of thefrequency swept oscillator in a time At. If the variation of frequencywith respect to time is constant, (such as it happens in anelectronically controlled system, with a sawtooth sweep) then V is alsoa constant. By making At equal to unit (one second) the velocity V canbe expressed as: the number of cycles of sweep during one second.

By continuously increasing the frequency velocity in a panoramicreceiver, the deflection produced by each signal becomes of a loweramplitude and has a tendency to spread in the direction toward which theband is swept.

This is due to the fact that a certaintime is required for signalseither to build up or to die out. If the sweep velocity is too great,the signal has no time to build up to lthe same amplitude as it wouldbuild by sweeping very slowly; on the other hand the circuits which havebuilt up a signal still retain signals after the cathode ray spot hasmoved away, on regions corresponding to other frequencies; this is whythe signal spreads out.

This is better understood by referring to Fig. 4. A panoramic receiver(or adapter) is periodically tuned from Fo to Fx cycles and the cathoderay spot on the screen moves in the direction of the arrow insynchronism with the periodic tuning. Curve a. shows the shape of thedeflection as the receiver is tuned through a signal at a velocity Vwhich should permit a dynami-c resolution r very nearly equal to p, thestatic resolution of the receiver. As the velocity V is graduallyincreased, the shape of the curve changes. While the spot risesfollowing the same curve as before, it rises to a lower amplitude andthen drops, trailing off further away along the frequency sweep axis.Curve b shows a condition where the value of p is only a small fractionof r. Curve c shows a condition where this condition is furtherexaggerated. The deflections spread along the screen, one deflectionmerging into another and the visual `discrimination between stationsbecomes impossible. When the deflections take such shape, the usefulnessof a panoramic receiver is greatly decreased.

From these curves, there can be derived a convenient definition for thefrequency resolution of a panoramic receiver, having a frequency sweepof a bandwidth w, a definition to which we will refer in our claims. Thefrequency resolution S is the difference of frequency, read on thecalibrated frequency sweep axis of a panoramic receiver sweeping afrequency bandwidth of w cycles, between two points on the deflectionproduced by a single signal, which are at '70% of the maximum amplitudeH of that deflection. This resolution is represented on Fig. 4 in dottedlines for each curve a, b and c, as Se, Sb, and Se. which are drawn at70% of the respective maximum amplitudes Ha, Hb, and Hc. The resolutionS measured in cycles represents the square root of the sum of twofactors: the square of the static resolution p defined above, and thesquare of the dynamic resolution r. ,The latter varies proportionally tothe frequency velocity V.

It can be seen from this that the resolution improves (S decreases) as Vdecreases, but can never be better than the static resolution P. Thisstatic resolution, however, is also tied up to the dynamic rsolution r,as it will be shown below. If the selectivity of the circuits is toogreat, the signals do not build up to a suillcient amplitude and thereceiver will not operate properly.

Practical tests show that the value of K, for the above definition of Sis very nearly equal to 2. In other words, 1=\/2 l and s=\/p2+2v (2) Theshape of the deflections is generally quite satisfactory provided .thatthe static resolution p is not smaller than about V5 of the r corre- -1spending to the highest velocity V required:

On the other hand, the velocity V can be expressed (when V is constant)as V==Wf (4) in which W vrepresents the visual bandwidth covered in onecycle of sweep and f the number of cycles of sweep per second (sweeprate).

Therefore,

S=\/F+2wf (5) The maximum value of W determines the value:

in the condenser C will be disturbed.

If the frequency sweep of that same receiver is reduced to 1 mc. (10cycles) the resolution S=1l.8 kc. At 100 kc. bandwidth, S=5.60 kc.

The resolution has improved considerably as the visual bandwithwasreduced, but it never can exceed the static resolution 4.4 kc. whichwas determined by the Wm required.

If the panoramic receiver, however, were designed to cover only 100,000cycles maximum bandwidth, ory less, p could be only 692 cycles. 'I'hetotal resolution S of the receiver in this case would be 3.50 kc. at 100kc. visual bandwidth and only 2.53 kc. at kc. bandwidth.

When a panoramic adapter for an ordinary broadcast band super-heterodynereceiver is to be designed, it is possible to cover a bandwith of about100 kc. or thereabouts. Such adapters can be designed to give therelatively high resolutions indicated above. 'I'he maximum bandwidth isa function of the intermediate frequency of the receiver and of theamount of preselection of the receiver used.

From Fig. 1, it can be seen, however, that the Tunable channel and the"'Panoramic channel, combined constitute a complete doubleconversionpanoramic receiver, in which the visual bandwidth W is not dependentupon the manual tuning adjustment. A

Such a receiver can be designed to cover any desired portion of thefrequency spectrum, with the limitations of resolution explained above.

In wide band monitoring systems. it is therefore advantageous to useseveral such wide band panoramic receivers to cover "roughly" the wholedesired portion of the frequency spectrum, and a plurality of narrowerband, high resolution, combined aural-panoramic receivers for inspectingthe regions where stations are indicated by the V,wide band receivers.

The combination of two screens, one for wide band, low resolution andthe other for narrow band, high resolution, is very practical foraccurate monitoring of the spectrum. One single tunable channel as shownon Fig. 1, followed by an Aural channel" can feed signals into twoparallel visual channels: one of high resolution and the other of lowresolution. One screen may cover, for example, a two megacycle band witha resolution o1' 20 kc. and the second screen a band of 100 kc., that is5% of the first screen. with a resolution of 4 kc. What may appear as asingle signal in the flrst screen may be resolved into a number ofseparate signals in the second one.

With the use of variable selectivity I. F. transformers in the 2nd I. F.amplifier, it is possible to design a more lflexible apparatus.adaptable for any type of service.

For wide visual bandwidth. the equipment as above described may bedesigned with a special wide-band R. F. amplifying system in the manualtuned channel of Fig. 1. This R. F. system may comprise wide bandpassfilters tuned by the manual tuning control, and proportioned so as tohave a fiat-topped amplitude-versus-frequency characteristic. In thiscase the panoramic channel of Fig. 1 may also be provided with yan inputbandpass I. F. amplifier having a flat-topped characteristic, tocooperate properly with the manually tuned bandpass channel. e

it has beenv shown, the resolution of -a panoramic receiver is afunctionof the frequency sweep velocity. By varying this velocity during eachcycle ofsweep, it is possible to vary the resolution over variousportions of the visual bandwidth shown on the screen. In anelectronically controlled panoramic retions will remain unchanged,lprovided that the same waveform is applied to both frequency controllingelement in the receiver and to one set of deflecting elements of thecathode ray tube. One type of waveform which will produce a higherresolution in the center of the screen than on the sides is illustratedin Fig. 5, wherein curve a shows a few cycles of sawtooth voltageplotted versus time. Curve b shdws a few cycles of sine wavesynchronized in phase with the voltage shown in a. Curve c showsthe-voltage resulting by adding the two voltages shown in a and b. Itcan be seen that the resultant voltage rises first steeply, then muchslower and then. toward the end of the cycle it rises again steeply.

' ordinary super-heterodyne radio receiver.

` transformer,

4the sawtooth and the sine wave. it is possible to obtain any desiredvariation in the frequency velocity. If the velocity is slowed down tozero in the center of each cycle, this velocity is doubled at theextremities. The resolution S will, therefore, be at the center equal tothe static component p whereas at 'the extremities Will be S=\/P+4V.Such a distribution of signals has the advantage that the signals whichare under closest scrutiny appear clearest and most accurate. Thisresult isobtained simply by inserting into the output of the square-wavegenerator a sine wa-ve circuit which may be taken from the source ofpower for the receiver. A phase adjusting bridge is generally requiredto bring the sawtooth and the sine wave in zero phase relationship.

Fig. 6 shows al schematic diagram of an electronically controlledpanoramic channel as shown in Fig. -l, and the electrical connectionsrequired to make it operate in cooperation with an An antenna I is shownconnected to the conventional super-heterodyne receiver 2, comprising atunable channel and an aural channel. A mixer tube 3, an aural I. F.transformer 4 and an intermediate frequency amplifying tube 5 are shown.The bandpass input transformer 9-I0 of the panoramic' channel isconnected to the plate of the tube 3 through a condenser 6 and aresistor 1. The signals from the mixer tube 3 are fed into a bandpassamplifying tube Il of the panoramic channel through a transformer Whosecoupling between primary 9 and secondary l0 is pre-adjusted or isadjustable to give it the desired bandpass characteristic line. Thisamplifier tube I I is not needed and the signals can be fed directlyinto the second mixer tube I8. Its presence, however, allows greaterpeak to peak amplitude ratios of compensation such as shown on Fig. 2,for wider bandwidths to be analyzed. The output of the tube II is fedinto a similar type of I4-I5. Both transformers are tuned to the desiredfrequency by means of variable condensers |2-I3 and l6-l1 respectively.If it is desired to keep the aural band of the receiver fixed in thecenter of the cathode ray screen, the mid-channel frequency of thesetransformers must be made the same as that of transformers 4 in thereceiver. However, for some purposes it may be desired to shift theaural channel over another region of the screen, or to change the shapeof the radio frequency response of the adapter. The condensers |2--I3and I6-I1 and/or the coupling of the transformers can then be brought onthe front panel of the adapter foi` the desired adjustment.

The. signals fromtransformer I 4-I5 are fed into the mixer tube i8together With the signals from the oscillator 21. The frequency of thisoscillator is periodically varied, preferably equally on each side of amean frequency F0, over a total width of W cycles (from 'I'his frequencysweep is obtained by means of a frequency controlling tube 28 and aproper phaseshifting network 29, 30. The frequency sweep rate (number offrequency sweeps per second) is determined by the frequency of asawtooth voltage, generated by the tube 3B after coupling yto the tube31. This voltage is applied to the grid of the frequency controllingtube 28 through the potentiometer 35 from the low impedance cathode oftube 31. The amount of frequency sweep (determining W) is adjustable bymeans of this potentiometer. The value of the mean frequency Fo isdetermined by the adjustment of condenser 59. The sharp intermediatefrequency amplifier following the second mixer is constituted of inputtransformer l3-20, amplifying tube 23 and the output transformer 24-25.The detector and amplifier is constituted of diode-triode tube 25.

\ Pulse automatic amplitude control.-In certain of panoramic receiversit is necessary to types signals differing in simultaneously comparestrength over wide ranges. Due to the dimensional limitations of ascreen, if linear amplification is used, this could not be possible; forexample, on a screen permitting a. maximum deilection of 2 inches and onwhich the smallest distinguishable signal is of 0.1 inch, it is possibleto compare only signals having a 20:1 ratio.

By using ordinary automatic volume control systems, having a long timeconstant, the strongest signal will generally determine the sensitivityof the receiver so that weak signals will not appear in the presence ofstrong ones. This condition is desirable for certain types ofapplications but it is not desirable in intercept or monitOring work.

A new improved system of automatic volume control described as pulse A.V. C. is shown on Fig. 6. Instead of applying the D. C. potential,obtained from the rectification of the carrier voltages to the grids ofthe amplifying tubes, we apply the rapid A. C. pulses created during thesweeping through the various signals, to those amplifying tubes,therefore, obtaining instantaneous variations of sensitivitycorresponding to the signal strength of each signal. Tube 39 is coupledthrough condenser 32 to the output of the 'detector 26 and apotentiometer 40, in its cathode is used to obtain the desired amount ofpulse A. V. C. voltage, which is applied to control the bias oiamplifying tubes Il and 23. The stronger the pulse, the greater thecontrol and the amplitude of the deflections will vary in a logarithmicratio on the screen, permitting comparison of signals having a ratio of200: 1 or more. The purpose of the coupling tube 39 is to obtain theright polarity for the controlling voltages required.

A manual gain control is provided by means of potentiometer 4Icontrolling the cathode returns of those same amplifying tubes. Theoutput of the tube 26is D. C. coupled to deecting element 42 of acathode ray oscillograph tube through potentiometer 52. This D. C.coupling is preferable to an A. C. coupling (through condensers) becausethe frequency sweep axis remains quite steady and unaffected byvariations of amplitude of the signals received; The same results can beobtained by inserting between the output of tube 26 and the deflectingplate 42 one or several stages of D.'C. coupled amplifiers. The outputof sawtooth amplifier 31 is connected to deilecting element 43, which isnormal to 42, through potentiometer 42', which permits adjustment of thelength of the line on the screen.

The above instrument is, as said above, limited to a visual bandwidthcorresponding to a certain extent to the pre-selection characteristicsof the cooperating receiver.

Fig. 'l shows a schematic diagram of a complete panoramic receiverhaving a wide visual bandwidth, incorporating a manually tunable powerin channel, a panoramic channel and an aural channel. Each of thesechannels is surrounded by dotted lines. The tunable channel includesganged condensers 45-46-41. The condensers M are tuning a band-passtransformer including coils 54-55 and an adjustable coupling vconnectedto the output of mixer tube I, just as the visual channel was connectedin Fig. 8. It must be noted that several such aural channels can beconnected in parallel. By tuning their respective transformers 4 and 50of each channel to slightly different frequencies, various portions ofthe visual band will through those channels.

By ganging the condensers tuning these transformers, it is possible tolisten at will to any signal visible on the screen, without touching thetunable channel (condensers 45, 46, Il). Instead give aural responses ofganging the condensers, a third converting' stage can be used, and inthis caseonly an oscillator requires tuning.

lThese schematic diagrams have been given only as speciilc examples ofmanners of obtaining the desired results, being quite natural that theresults desired can be obtained by many modifications of those diagrams.

Instead of electronic frequency sweep, mechanical sweep can just as wellbe used, such as rotating condensers, inductances, or other methods suchas described more in detail in previous patent applications.

One practical way of obtaining a frequency sweep in step with a sourceof alternating voltage. is by means of a special synchronous vibratingcondenser.

Figs. 8a b, show the construction of such a vibrocondenser. Alternatingcurrent is fed into the exciting coil 80 through leads 66, 61. A softiron core or a permanent steel magnet 69 inserted in this coil createsan alternating magnetic field at its ends. A vibrating steel reed 6| isplaced in this field. This will vibrate in step with the magnetic forcesproduced and will be attracted and repulsed in synchronism. By using asoft iron core, the number of vibrations will be equal to double thefrequency of the.l voltage applied. whereas by using a permanent magnetcore the magnetic eld is neutralized during half of the time. and thenumber of vibrations is equal to the frequency of the alternatingcurrent. The

reed il is fastened in the` base of S4 of the instrument by means ofblock 1i, and on the free end one or more parallel condenser plates 62a,b, c. are mounted normally to its surface. These constitute the movingarmature of a capacitor. The other armature is fixed and consists ofstator plates 63a. b, c, d, which are insulated by means of insulatingblock 65. 'Ihe dimensions and weight of the reed and moving armature areso proportioned that its natural period of resonance is very nearly thatat which it is made to vibrate. 'I'his reduces the required amount* ofexciting the coil 60. This period is adjustable by means of a screw 68mounted on the extreme end of the reed, which varies slightly itseiective length. We iind it ,advantageous to slightly dampen thevibrating reed by, for example. inaerting a sheet of rubber 1I. betweenthe base I4 and block 1I. While this arrangement requires a little moredriving power, the amplitude and phase relationship with the driving A.C. voltage remain more nearly constant even .if the frequency of the A.C. varies noticeably.

. Fig. 8a shows in full lines the reed in stationary positioncorresponding to capacity C0, and in dotted lines fthe reed in extremevibrating positions, corresponding to capacities Cm and Cmm. It can beseen that it is possible to make this variation equal in each direction(Umax-CoCo-Cinin) or to give, according to the shape of the plates, anydesirable variation of capacity versus amplitude of vibration. Such acondenser will vary in step with the A. C. voltage applied. In case of asine wave, its instantaneous velocity will also vary according to'alowest, passing through zero, correspondingto capacities is the highestin the central ing to capacity Co. This maximum velocity Vmx=1rV. inwhich V is the average velocity, corresponding to the frequency of thesine wave.

Figs. 8b and 8c show respectively an end view and top view of thealternating condenser.

Such a condenser can be used to replace the condenser 59 in Figs. 6 and7. In this case, there is no need of the reactance tube 28. The designcan be still further simplined by eliminating the sawtooth generator- 38and ampliiler 31. The horizontal deflecting element 43 of the cathoderay oscillograph can bethen energized directly with the A. C. currentfrom the same source which energized the synchronous vibratingcondenser, as it will be shown on Fig. 9.

Due to the fact that the motion of the con denser is reciprocating, itis sometimes diillcult to make the capacity variations in both strokesabsolutely equal. In other words, there may exist a variable phasedifference between the sine wave producing the capacity variation andthat producing the sweep on the screen; this phase difference may'change as the reed moves toward the coil, or away from the coil. Such achange will cause the image on the screen to appear blurred or double.

In order to avoid this condition, this phase difference must either becycle of the image must be blanked out, by apat the extreme ends Cmlnand Cmax and it position correspondblanking potential during each halfcycle of sweep. This will be shown in Fig. 9.

The advantage of the synchronous vibrating condenser is the greatsimplicity it ailords for making a panoramic receiver. ABy inserting avoltage controlling device in the exciting coil Il, the amplitude of thevibration can be so varied that it is possible to vcover wider ornarrower visual bandwidths at will.

Due to the fact, however, that the instantaneous velocity of the reedvaries, the resolution will be unequal, the maximum resolution beingshown at the extremities of the screen and the lowest resolution in thecenter.

Such a vibrating condenser, with a. cathode ray oscillograph, canconstitute a simple attachment to any ordinary type of receiver whichwill become a panoramic type receiver, or aural reception receiver, atwill.

sine wave. '1"he velocity is I other is oil was pointed out above;

Fig. 9 shows the essential parts of such acomblnation. 15 represents alconventional radio receiver having a manually tunable condenser 18. Inparallel with this condenser is connected a vibrating condenser 82-63.The exciting coil voltage is derived from the secondary 11 of a powersupply transformer through a switch 18 and a potentiometer 19. 'I'hiscontrols the ainplitude swing of the vibrating reed 6l. The output ofthe receiver is connected to an aural device 88, and a switch 85 isprovided for interrupting its operating when the vibro-condenser is inoperation. Switches 18 and 85 can be operated simultaneously: when oneis on the and vice-versa. The Vertical deflecting element 42 is alsoconnected to the output of the receiver (detector or audio frequencyamplifier). The horizontal element 43 is connected to the secondary 80of the power supply transformer, through a phase shifting bridge 8|-8I,which shifts the phase by 90. This is necessary l"because the vibrationof the condenser varies in phase with the current variation which is 90out of phase with the voltage variation. From the same power supplyvoltage the blanking wave is supplied to the grid 88 of the cathode raytube through condenser 89, as described above.

Ihe contro1s19 and 16 can be ganged together if desired, and the valueof the potentiometer 19 can be made such as to maintain a substantiallyconstant visual band width 'as the condenser 18 is rotated from minimumto maximum.

What has` been said about a vibrating condenser can be said about avibrating inductance. Instead of moving the armature of a capacitor, thereed can move one or several iron cores in one or several coils. Thecombination of a variable capacitor 18 for manually tuning the receiver,with a periodically varying inductance has the advantage that the visualbandwidth W varies proportionally directly to the frequency rather thanto the cube of the frequency as it this proves important for specialapplications.

As it has been pointed out, the combination between tunable channels,aural channels and a panoramic channel, can be extended further, to morecomplex combinations.

In the patent applications of Marcel Wallace Nos. 196,520 (Patent2,219,151, supra) (Figs. 22, 23 and 37), 330,763 (Fig. 25) filed April20, 1940, for Radio beacon altimeter and panoramic reception system,Patent 2,312,203, and 357,814, filed September 21, 1940, for Radioaltimeter and panoramic reception system, it has been shown that due tovisual retentivity, it is possible to use one panoramic visual receivingchannel to simultaneously show different portions of the frequencyspectrum on two different display surfaces.

Either mechanical or electronic switching methods have been shown inthose applications to effect the synchronous operation of alternatelyselecting two different inputs (coils or antennas) and separate theoutputs on two regions of the screen. l

The same methods can be used by substituting two different Tunablechannels in the place of two different antennas or coils, and

either show them on two portions of acathode ray screen, or on twoseparate screens. An example of such a combination is shown in Fig. 10in which two tunable channels are shown, operating to cover two bands ofthe spectrum: one for example from -130 mc., taking the airway beacons,which may be manually tuned; and another from 148-154 mc., coveringvertical separation indicating beacons (such as described in application357,814) and which may be tuned by an vaneroid cell. Each of the outputsof these two channels is passed through a coupling tube into a Panoramicchannel. These coupling tubes are alterately blocked by means of asquare wave voltage alternately applied to their grids, and acttherefore as electronic switch No. 1 shown on Fig. l0. The square wavevoltage generator, also shown, is synchronized with the sawtoothvoltage'generated in the panoramic channel. The panoramic channel can beterminated either with two separate cathode ray tubes, or with onesingle cathode ray tube, as shown in the previous patent applications.

In the first case each tube is bianked out alternately by applyingthrough an appropriate coupling device square wave voltage on theirgrids, in synchronism with the same square wave generators. Thiscoupling device is shown on Fig. l0 as electronic switch No. 2; in thesecond l case,` the vertical deflection plates receive the square wavevoltage so as to produce two parallel lines on the screen of the tube,corresponding to the two frequency sweep axes of the two channels.

As an addition to this combination, an Aural channel is shown, which canbe connected by a switch, at willY to either of the two tunablechannels, so that the operator can listen to the signals in the centerof the screen on each channel.

While in this specification, and in some of the appended claims, we havereferred to an aurally responsive means it is to be understood that suchmeans may be any device, whether acoustic or electric, which may be madeto respond or indicate the presence of an audio modulation, such asalternating current meters, rectifiers coupled to D. C. ammeters, vacuumtube voltmeters, etc. Such devices are sometimes also referred to, inthe appended claims, as: audio responsive means." J

While we have described our invention in certain preferred embodimentswe realize that modications may be made in the circuit arrangements anddisposition of elements of apparatus and we vintend no limitations uponour invention other than may be imposed by the scope of the appendedclaims.

What we claim as new and desire to secure by Letters Patent of theUnited States is as follows:

1. A signal receiving system adaptable to be connected to asuperheterodyne radio receiver having a signal selecting circuit and anintermediate frequency amplifier and an audio responsive device, asource of periodically varying voltage and electronic means controlledby the said varying voltage for periodically and automatically tuningthe said signal receiving system over a wide frequency band extendingequally above and below the frequency of the said amplifier, means foramplifying the ends more than the center of the said wide band so as tosubstantially compensate for the sharpness of the said s'gnal selectingcircuit, and visual means operated in synchronism with the saidperiodically varying voltage for reproducing on a screen, in spacedrelationship corresponding to their respective frequencies andamplitudes, the signals receiv- 'able over the said frequency band, saidvisual means operating simultaneously 'with and independently of thesaid audio responsive device.

2. A radio receiving system for simultaneously indicating the amplitudeand frequency characteristics of all signals within a continuous butselectable band of the frequency spectrum, as well as the modulation ofone of said signals, said system including an input channel, a manuallytunable oscillator and a frequency converter, a signal-amplifying systemtuned to a predetermined frequency and connected to the said converterfollowed by a detector and aurally responsive means connected to thesaid detector; a second signal amplifying system connected to the saidfrequency converter, means for periodically tuning the said secondsignal amplifying system over a wide band of frequencies extendingequally above and below 'the said predetermined frequency, means forvarying the width of the said wide band, and visual indicating meansoperating in synchronism with the said means 'for periodically tuningthe second signal amplifying system, for indicating on a display surfacein spaced relationship corresponding to frequency relationship, thesignals present on the said wide band of frequencies, said auralresponsive means and said visual means operating simultaneously andindependently of each other.

3. Method of simultaneously observing the frequency and amplitudecharacteristics ofv all'signais present over a manually selectable bandof the frequency spectrum, extending on each side of an vaurallyreceived signal, with the aid of a tunable radio receiver provided witha signal conversion stage and terminated with aural reception means,including the following steps: deriving from a signal conversion stageof a manually tunable radio receiver all the signals present over a wideband of the frequency spectrum, periodically and successively selectingeach elementary portion-of the said wide band including an aurallyreceived signal at a predetermined sweep rate, amplifying each of thesignals successively received at different degrees of amplification soas to compensate for the selectivity ofthe said receiver, detecting thesaid signals and visually indicating in spaced relationship according totheir corresponding frequency relationship and at a rate equal to thesaid sweep rate, the amplitude of each Vof the detected signals.

4. A system for visually analyzing a continuous band of the radiofrequency spectrum, of substantially constant and predeterminedfrequency bandwidth, said band being selectable over a wide range of the`spectrum, said system including an input channel followed by a firstfrequency conversion stage, a ilrst oscillator connected to the saidfirst frequency conversion stage, means for tuning said oscillator, asecond frequency conversion stage coupled to the rst, said secondfrequency conversion stage being tuned to accept a band pass equal to orgreater than the bandwidth to be analyzed and coupled to the said firstfrequency conversion stage, a second oscillator connected to the saidsecond frequency conversion stage, automatic means for periodicallyvarying the frequency of the said second oscillator over a bandwidthequal to the bandwidth to be analyzed, an amplifier tuned over a narrowbandwidth representing only a fraction of the bandwidth to be analyzedand connected to the output of the said second conversion stage, asource of periodic sweep voltage operating in synchronism with the saidautomatic means and visual means operated in synchronism with the saidsweep voltage for representing on a display surface in spacedrelationship' according to their frequency difference the signalspresent over the band to be analyzed,

said band remaining of constant width independently of the frequency ofthe said first oscillator.

5. A system for visually anahfzing a continuous band of the radiofrequency spectrum, as set forth in claim 4, wherein a ilxed frequencycalibrated scale is mounted in ilxed relationship with the said displaysurface, for reading directly on the said scale the frequencyrelationship between the signals appearing on the said surface,independently of the position of the tuning means of the said receivingsystem.

6. A system for visually analyzing a continuous portion of the radiofrequency spectrum, as set forth in claim 4, wherein means are providedfor vadjusting at will the frequency bandwidth of the said periodicallyvarying oscillator.

7. A system for visually analyzing a continuous band of the radiofrequency spectrum, as set forth in claim 4, wherein an aural channelincluding a sharply tuned intermediate frequency amplifying stage iscoupled to the output of said rst converter, said intermediate frequencystage being coupled to a detector, followed by an audio responsivedevice, whereby the said device operates simultaneously with. andindependently of the said visual means.

8. Method of visually analyzing a band of the radio frequency spectrumhaving diiferent degrees of frequency resolution over its range, withlthe aid of a tunable radio receiving system and a cathode ray tubehaving a cathode ray generator and a screen, including the'i'ollowingsteps: proquency band in synchronism with the said periodically varyingvoltage, adjusting the rate of change of said varying voltage and ofsaid tuning so that the regions of the band requiring the greatestresolution are tuned through at the slowmeans operating in synchronismwith the said automatic means. j,

10. A radio receiving system as set forth in claim 9, wherein the saidinput channel has a wide bandpass characteristic and is" tunable withinpredetermined limits of the frequency spectrum. f l

11. A panoramic ing a signal input channel, a first oscillator, Vmanualmeans for tuning said oscillator over a predetermined range of thefrequency spectrum, a first frequency converting stage coupled tosaidinput stage and to the said first oscillator, a second oscillator,automatic means for periodically tuning said second oscillator withinpredetermined limits o f the frequency spectrum, adjustable means forvarying the limits of the frequency spectrum between which the saidsecond oscil lator is periodically tuned a source of periodicallyvarying voltage operating in synchronism with the said last means, asecond frequency converting stage coupled tothe said first convertingstage and to the said second oscillator, a signal amplifier coupled tothe said second converter and a visual output device coupled to the saidamplifier and to the said source of periodically varying voltage. .l

12. Radio receiving system including va, signal receiving circuit,automatic means forA periodically tuning said signal receiving circuitover a predetermined frequency bandwidth, an amplifier coupled to thesaid signal receiving circuit, a detector coupled to the said amplifierand producing a series of electric pulses ofa duration equal to and ofan amplitude proportional to the amplitude of the signalsl successivelyreceived, means for feeding back the said pulses into the said amplifierso as to reduce its amplifying char,- acteristics proportionally to theamplitudeof each said pulses and visual means operated inisynchronismwith the said automatic means for'representlng on a display surface eachofthe said signals successively received, in the form ofvisual radioreceiving system includchannel, adaptable to be operated in conjunctionwith a superheterodyne radio receiver, said ref ceiver having a signalselecting means, frequency conversion means, an intermediate frequencyamplifier tuned to a frequency Fi, and audio responsive means, in theabove order, and the said panoramic channel comprising: input means,including a bandpass filter for coupling the said panoramic channeltothe said frequency conversion means, said filter means being tuned topass a band ,of frequencies centered at frequency Fl and exten ing overa width greater than w/2 cycles, on each side of frequency Fi, thepassband characteristic of the said filter being non-linear andsubstantially compensating for the sharpness of response of thesaidsignal selecting means, means for automatically and periodicallytuning the said panoramic channel over a frequency band having a'constant width of w cycles and extending equally on each side of thesaid frequency, and visual means operating in synchronism with the saidperiodically tuning means, for indicating on a display surface, inspaced relationship corresponding to their frequency and amplituderelationship, the signal present over the said band of constant width,said visual means operating simultaneously with, and independently of,the said audio responsive means.

16. A panoramic receiver having a constant bandwidth, including a signalpre-selector circuit, means following the said circuit, including alocal oscillator for converting the incoming signals into signals havingan intermediate frequency, tuning means for the said oscillator, abandpass filter having its center frequency tuned to the saidintermediate frequency and having a non-linear amplitude characteristicto substantially compensate for the sharpness of the said signsseparated by linear intervals proportional to the respective frequencyintervals between the corresponding signals and at substantiallylogarithmic amplitude ratios. l

13. A panoramic radio receiving system whose center frequency is`tunable over wide, regions of the spectrum. and vwhich visuallylindicates a band of constant width .of w cycles, independently of theregion of the spectrum overv which it is tuned, said system including: aAtunable channel coupled to a panoramic channel, wherein the saidtunable channel includes a signal selecting circuit and a frequencyconverting circuit in the order named, tuningv means for the saidcircuits.

a bandpass filter means following the said converting circuit, saidfilter means being tuned to pass a iixed and predetermined band of thespectrum of a width greater than w cycles, said panoramic channelincluding automatic frequency scanning means covering a band of w cyclesand whose center frequency corresponds substantially to the center ofthe said predetermined band.

14. A panoramic radio receiving system, as set forth in claim 13,wherein the said bandpass filter means is coupled to an independentaural channel. including a signal amplifying circuit tuned to afrequency within the passband of the said filter, followed by a detectorand an audiovresponsive device, so that a signal shown on the panoramicchannel is simultaneously audible in the said audio responsive device.

15. A receiving system including a panoramic pre-selector circuit, saidfilter circuit being connected to supply said intermediate frequencysignals to a plurality of signal channels, one of said channels beingperiodically tunable over a band of constant width and situated withinthe pass band of the said filter, and meansfor visually indicating on adisplay surface all signals receivable within the said band of constantwidth, at intervals corresponding to their respective frequencyseparation, and another of the said signals channels including a filtermeans and a detector, in the order named, said filter means having apass range which is narrower than, butk situated within, that of thefirst ffllten said detctor being followed by an aural responsive dev ce.

17. A panoramic receiver having a constant bandwidth as set forth inclaim 16, wherein the pass range of the said filter means is situated inthe center of that of the first filter.

18. A panoramic receiver having a constant bandwidth as set forth inclaim 16, wherein the said filter means includes tuning means forsituating its pass range over` any portion of the pass range of thefirst filter.

19. The method of panoramic reception for securing an optimum degree ofresolution which includes: receiving a band of the spectrum of a widthof p cycles and periodically displacing this band, at a rate of f cyclesper second over a wider band having a width of w cycles wherein thevalue of p is made greater than V0.2 wf, converting all signals receivedover the said band of w cycles into visual signs and spacing the saidsigns lproportionally to theA difference of frequency betweencorresponding signals, the resolution between the said visual signsbeing of the order of VPH-2 wf.

20. A panoramic radio receiving system having an optimum degree ofresolution, including automatic frequency scanning means, said means peiriodically covering a band of the spectrum of a Width oi' w cycles andat a rate of f cycles per second, lter means following the said scanningrPatent N o. 2,381,940.

Certiicate of Correction August 14, 1945.

MARCEL WALLACE, ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,second column, line 18,

for the word unit read um'ty: page 4, first column, line 35, for theequation page 9, second column, line 48-49, claim 16, for signals read.szgnal: and that the said Letters Patent should be read with thesecorrections therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 1st day of January, A. D. 1946.

[sEALl LESLIE FRAZER,

First Assistant Commissioner of Patents.v

